The lifetime of traditional light sources, such as, for example incandescent, fluorescent, and high-intensity discharge lamps, are estimated through industry-standard lamp rating procedures. Typically, a large, statistically significant sample of lamps is operated until about 50% have failed, which at that point, in terms of operating hours, defines a “rated life” for that lamp. Decrease in lumen output may occur as a lamp or light fixture operates over a long enough period of time. Based on years of experience with traditional light sources, lighting experts often use lamp life ratings, along with known lumen depreciation curves, to design the lighting for a desired space, and to determine re-lamping schedules and economic payback. This aspect of predictive life, half-life or end-of-life of a light source is not particularly true with LED, which can continue to operate at very low light levels and are at less risk of critical failure compared to traditional light sources. An LED's end-of-life may be measured in terms of lumen flux (i.e., the quantity of the energy of the light emitted per second in all directions) depreciation to a particular level as defined by manufacturers or by standard test methods.
LEDs usually do not fail abruptly like traditional light sources; instead, their light output slowly diminishes over time. Furthermore, LED light sources can have such long lives that life testing and acquiring real application data on long-term reliability becomes problematic—for example, new versions of products are often available before current ones can be fully tested. To add more to the challenge, LED light output and useful life are highly dependent on electrical and thermal conditions that are determined by the luminaire and system design. This conclusion is reflected in a Philips Technology White Paper, titled “Understanding power LED lifetime analysis,” which may be found at www.lrc.edu/programs/solidstate/assist/index.asp (the “Philips paper”).
According to the Alliance for Solid-State Illumination Systems and Technologies (ASSIST), the threshold at which human eyes may detect light output reduction is about 70% lumen maintenance. Further research conducted by ASSIST shows that a 30% reduction in light output may be acceptable to a majority of those who use luminaires (otherwise known as lighting devices or lighting fixtures and is defined as a complete electric light unit, which includes any sort of light source—incandescent, fluorescent, high-intensity discharge lamps, LEDs, and the like) in general lighting applications. However, ASSIST recommends considering both higher and lower figures for lumen maintenance for certain types of applications. These applications may include, for example, wall-washing application where lights may be seen by users side-by-side, which may require that the useful life of the lumen to be calculated on a higher figure, such as, typically 80% lumen maintenance. In some applications where light outputs are not critical, such as, for example, decorative light systems, lower lumen maintenance thresholds may be acceptable. ASSIST has proposed that two coordinates be used to express the useful lifetime of an LED component, or system L70 and L50. Rated lumen-maintenance life is measured in hours with associated percentage of light output, noted as Lp. In other words, L70 of 30,000 hours means that the tested LEDs produce 70% of the initial light output at 30,000 hours. If an LED has L50 of 30,000 hours, its lumen output decays faster than one with L70 of 30,000 hours. Since the temperature of the device may impact these figures, thermal design of devices is critical but not necessarily enough to maintain lumen life absent other considerations. For example, dimming level and average power consumption of the lighting device, e.g., level of usage, may dictate its L70 and L50. Changes in power source current may also impact the L50 of the LED device. The same may be true for constant current, where temperature variations will impact the L50 number.
With reference to FIGS. 19 and 20, and further reference to the Philips paper, typical graphs of factors impacting LED lifetime are provided from the Philips paper. According to FIG. 19, if temperature is constant, changes in current will impact the L50 of the LED device. The same is true for constant current, (see FIG. 20, in this case 1.5 A), where temperature variations will impact the L50 number.
A disadvantage with current luminaire and/or LED systems and methods is that there is currently no standard format for reporting luminaire/LED lifetimes and/or lumen depreciation curves. According to a Paper published by the U.S. Department of Energy, titled “LED Luminaire Reliability,” and retrievable from http://ephesuslighting.com/wp-content/uploads/2014/01/Fact-Sheet-LED-Luminaire-Reliability.pdf, “A test procedure currently in development by the Illuminating Engineering Society of North America (designated LM-80, IESNA Approved Method for Measuring Lumen Maintenance of LED Light Sources) will provide a common procedure for making lumen maintenance measurements at the LED device, array, or module levels”. Further, the U.S. Department of Energy paper states: “The LM-80 test procedure addresses only one factor in the life of an LED luminaire—lumen depreciation of the LED device over the prescribed test period.” For LED light sources, LM-80 defines lumen-maintenance life as “the elapsed operating time at which the specified percentage of the lumen depreciation or lumen maintenance is reached, expressed in hours.” On the other hand, the rated lumen-maintenance life is defined as “the elapsed operating time over which an LED light source will maintain the percentage (p) of its initial light output” and is provided by the LED manufacturer. A disadvantage with this method is that there are usually many additional factors to consider when LEDs are installed in a luminaire or systems that can impact the rate of lumen depreciation or the likelihood of catastrophic failure, and this test method fails to address those additional factors. These additional factors may include, for example, environmental conditions of the environment in which the luminaire/LED is installed. The environment may be, for example and without limitation, a room, corridor, or other space in which light is required. Environmental conditions include temperature, humidity, barometric pressure, etc.
Other factors that can influence lumen maintenance are system conditions such as moisture incursion into electrical components, voltage or current fluctuations, failure of an LED driver or other electrical components, damage or degradation of the encapsulation material covering the LEDs, damage to the wire bonds that connect the LEDs to the fixture, and degradation of luminescent materials such as phosphors.
Since the emergence of LED lighting and its increased use in lighting applications, the lifetime of light sources has increased greatly, and lighting fixtures no longer require the old socket and bulb combination. Since LEDs are low-voltage light sources, they may require a constant Direct Current (DC) power supply (voltage and/or current) to operate at their optimal conditions. Operating at a low-voltage, the DC power supply acts as a barrier between an Alternating Current (AC) input and the LED. This barrier may increase the LED's resilience to different power levels and may help allow the LED safely withstand longer stand-by power. In a normal scenario, for example, individual LEDs may require 2V to 4V of DC power and several hundred milliamps (mA) of current to operate.
While LEDs may also help increase the lifetime of light sources greatly, the lifetime of the LEDs heavily depends on the driver because the driver will fail before the LED and the entire luminaire may then require replacement. Extending the life of the driver therefore extends the life of the LED and any other system components that would require replacement. For example, due to their physical makeup, LEDs must be protected from line-voltage fluctuations. Changes in voltage may produce a disproportional change in current, which in turn may cause light output to vary, particularly because LED light output is proportional to current and is rated for a current range. If current exceeds the manufacturer's recommendations, the LEDs can become brighter, which changes their color temperature, and results in faster degradation and a shorter useful life. The drivers used in luminaire and/or LED systems may be a crucial element in providing adequate protection from rapid and sudden voltage fluctuations in the LEDs by regulating the current that flows to the LEDs via converting incoming AC power to stable DC voltage during their operational period. Drivers may convert 120V (or 240V) or 60 Hz (50 Hz) AC power to low-voltage DC power required by the LEDs, and protect the LEDs from line-voltage fluctuations. Additionally, the drivers may be able to provide constant voltages, such as, 10V, 12V and 24V. The drivers may also be able to provide constant currents, such as 350 mA, 700 mA and 1 amp (A). Although there are some drivers that may be capable of operating with any commonly available LEDs, there are some drivers that are manufactured for use with only specific LEDs. For instance, some drivers may be designed to compressively fit inside a junction box, and may include isolated Class 2 output for safe handling of the load, operate at high system efficiency, and offer remote operation of the power supply.
The drivers used in luminaire and/or LED systems may enable dimming, color changing, and sequencing of, for example, LEDs in a constant and smooth manner. Since LEDs may be easily embedded with circuits that act as drivers to control dimming and color changing, these functions may respond to preset commands. Most of the drivers may be compatible with commercially available 0V-10V control devices and systems such as occupancy sensors, photocells, wall box dimmers, remote controls, architectural and theatrical controls, and building and lighting automation systems.
Due to the large business opportunity in the LED enabled lighting technology market, there are a large number of LED manufacturing companies, each having their own specially designed drivers for use with related luminaires/LEDs and associated equipment. These companies may provide a nonstandard set of specifications that define normal operational ranges for the LEDs and the drivers. These specifications, in most cases, include the maximum temperature the driver can sustain to keep the LEDs operational, the maximum number of ON/OFF cycles the driver can withstand before it fails, the maximum voltage level the drivers can handle, etc. In many cases, the manufacturer may disclose prediction curves related to different characteristics of each of the drivers.
Driver reliability and lifetime may be linked to the operation temperature to which the driver is subjected as shown in the chart in FIG. 21. For each driver, manufacturers may provide/state an allowable ambient temperature operating range (ta) and a maximum capacitor temperature (tc) for the driver. The ambient temperature is typically in the range of about −20° C. to about +60° C. The capacitor temperature may sometimes be referred to as “case temperature” and is usually an alternative to measuring the ambient temperature. The case temperature may allow a more accurate reading of the temperature of the components within the driver, and may make it easier for customers and/or end users of the driver to test the capacitor temperature without having to disassemble and/or open the driver. The manufacturers of the drivers may also provide the maximum temperature to which output capacitors located on the driver can be subjected. The output capacitor is one component that may limit life span of the driver due to the capacitor type used at the output phase, such as, for example, an aluminum electrolytic capacitor.
Numerous luminaire drivers may use aluminum electrolytic capacitors as part of the output phase circuit to reduce the ripples in current supplied to the LEDs. It is believed that increasing the output capacitance will reduce the ripple current. On the other hand, a failure of an aluminum electrolytic capacitor may result in decreased output of its capacitance and a corresponding increase in ripple current. For example, a 50% reduction in performance of the output capacitor can result in double (two-fold) the amount of ripples (changes) in the current that is being supplied to the LED by its defective driver.
Aluminum electrolytic capacitors are typically made up of three layers: 1) an anode aluminum foil that is etched and covered with an aluminum oxide, 2) a spacer made of paper that is saturated in electrolyte; and 3) a cathode aluminum foil. A primary cause of reduction in capacitor performance is heat, because raised/increased temperatures may lead to drying out of the capacitor. FIG. 22 is an exemplary chart showing the degradation of an aluminum electrolytic capacitor life as a function of capacitor temperature in different brands/types of capacitors represented by the red, blue, and green lines. The causes of temperature increases within the capacitor include over-volting the capacitor, which may be caused by poor circuit design, and exposing the capacitor to high ambient temperature. In some instances, over-volting a capacitor leads to catastrophic failure.
Other factors that may affect the lifespan of a driver are, e.g., the number of ON/OFF and/or dimming cycles, the amount of current used by the luminaire and/or driver, and the applied voltage at the luminaire and/or driver. FIG. 23 illustrates a diagram of the dimming level and associated power consumption of a luminaire over time, and may be used to predict which luminaires are likely to fail based on the manufacturer's data regarding cycles, voltage, current, etc.
The effect of switching cycles, that is, turning the current on/off, in drivers may be solely dependent on the luminaire driver itself. While a minimum standard criterion is set for driver manufacturers to achieve, manufacturers may provide their own specifications that are usually supported by long-term testing of their products. A disadvantage with use of switching cycles, is that they may often introduce negative effects on the drivers due to thermal shock on the capacitors and inrush current/input surge current.
Many of the challenges with the luminaire and/or LED drivers may be due to the installation environment and wrong installation set-ups. For example, when there are not enough drivers to support the number of LEDs linked/coupled together to create a lighting environment, there may be a high load on the drivers. If a wrong driver is selected, the driver will need to operate outside its recommended limits. In addition, if the LED is placed in a cold environment, it will draw more power, which may lead to rapid reduction of the life cycle of the LED.
A need exists for a solution for proper handling of LED and luminaire drivers, and proper enhancement of useful life span of LED and luminaire drivers. Furthermore, while manufacturers are making state of the art LEDs and their different components, including the drivers, there remains a need for a clear and/or embedded solution that can predict the half-life of the luminaire and/or LED system in advance. While effective manufacturing processes, installation, and use of LED systems may help dictate its half-life, the half-life is not well predicted. Therefore, there is a need for a system and a method to predict the half-life and/or end of life for the drivers and LEDs, and that is fully integrated and constantly monitors failure indications, prior to a failure occurrence in the LED system. Further, there is a need for a system that monitors multiple variables of luminaire and/or LED drivers, as well as the LED light intensity depreciation of LEDs, and combines the results in a single system to ensure that the shortest half-life prediction of the LED and/or luminaire driver is known.
Considering the above background, devices, systems, and methods that are enabled by technologies local to a luminaire/LED, or by Internet of Things (IoT) networks and servers, are disclosed to provide an accurate and cost effective solution for predicting the half-life of luminaire/LED lighting systems, including drivers, and maximizing the useful life of such lighting systems.